Modular active test probe and removable tip module therefor

ABSTRACT

A modular active test probe and removable tip module therefor. Within the scope of the invention, there is a probe tip module comprising a first probe tip adapted for probing a circuit under test to receive a signal therefrom. The probe tip module includes an amplifier having a first input solidly connected to the probe tip, an output connected to an output connector, and a housing for supporting the probe tip, the amplifier, and the output connector. A probe body is cooperatively adapted with the housing for repeatably removably receiving at least the output connector.

This application claims the benefit of the provisional application Ser.No. 60/340,495 filed Dec. 14, 2001, entitled Modular Active ElectricalTesting Probe, which is incorporated by reference in its entirety.

BACKGROUND OF INVENTION

The present invention relates generally to a modular active test probeand a removable tip module therefor that optimizes test probeperformance.

Test probes are particularly critical to the accurate measurement ofsignals. As is well known, test probes are used to make temporaryconnections between a circuit test point and a measuring instrument,such as an oscilloscope. The primary goal when measuring a signal is toobtain as accurate a measurement as possible without disturbing theoperation of the circuit. Specifically, the goal is to sample a signalwithout unduly loading the circuit while maximizing signal fidelity. Forpurposes herein, signal fidelity refers to the accuracy with which thesignal that would be present at an unloaded test point is transmitted tothe measuring apparatus and is achieved by, among other things,minimizing signal attenuation, maximizing bandwidth, providing constanttime delay with increasing frequency, and minimizing ringing, signalreflection, and other types of signal distortion. To design a test probethat is capable of satisfying this goal, the properties of the testprobe, the probe cable, and the measuring instrument must be consideredtogether.

It is also important when measuring signals to have a test probe that isadapted to specific measurement needs. First, different test instrumentshave different input requirements, e.g., bandwidth, input resistance,and input capacitance and the test probe and probe cable used with aparticular test instrument should be compatible with these requirements.Second, different test probes are adapted for sampling different testconditions. Voltage probes may be adapted for measuring high frequencyor differential signals. Test probes may be adapted to the specificgeometries or electrical characteristics of the circuit being tested.For example, some circuits now employ a standard connector for attachinga test probe. Moreover, test probes may be adapted to measure differenttypes of signals, such as current or optical signals.

Test probes typically include a probe tip that makes physical contactwith the test point, a probe body that allows the test probe to be heldand which also holds the probe tip and probe circuit components, and aprobe cable used to couple the test probe to the test instrument. Anactive test probe additionally includes a high input impedance amplifierto provide high signal fidelity while minimizing loading of the circuit.

Typically, the probe body and probe tip are integral. However, in sometest probes, the probe tip can be removed from the probe body andreplaced with another probe tip. A removable probe tip is desirable forseveral reasons: (a) different types of probe tips are required or maybe advantageous for different test conditions; (b) the use of a singleprobe and several removable probe tips of different types is lessexpensive and more convenient than using several different complete testprobe assemblies; and (c) if the removable probe tip breaks, it is lessexpensive to replace the probe tip rather than the complete test probeassembly. Though removable probe tips are desirable, they suffer from anumber of disadvantages.

As mentioned, the design of a test probe capable of sampling a signalwithout unduly loading the circuit while maximizing signal fidelityrequires that the test probe, probe cable, and test instrumentproperties be considered together. For example, the circuit elements inan active test probe are typically designed to optimize the performanceof a probe tip having a particular geometry. However, these same circuitelements will not provide optimal performance when a probe tip having adifferent geometry is substituted. In other words, a test probe may bedesigned to optimize the signal fidelity for a single probe tip, butsignal fidelity will not be optimal if the test probe is used with anumber of different probe tips.

Other disadvantages of removable probe tips arise from the fact thatremovable tips require at least one (and typically more than one)removable connection or connector in the signal path. The connectors areneeded to mechanically join and electrically couple the probe body andthe probe tip. One common type of electrical connector is a socket onthe probe body that receives the probe tip. Within the socket is apliant spring or elastomer that compresses to receive and engage theprobe tip after it has been inserted. The socket, the probe tip, andspring are all made from conductive material, such as metal. The socketis coupled to probe circuitry within the probe body and electricallycouples the probe circuitry with the probe tip. In another common typeof electrical connector, threaded members, such as male and femalecoaxial cable connectors or a threaded probe tip and socket, are used tojoin the probe tip and the socket together. The threaded connectiongenerally holds the probe tip rigidly, but employs more metal than isused in pliant connectors.

The mechanical requirements for removably coupling metal parts typicallyincrease the use of conductive materials and thereby increase theparasitics of the test probe, which degrades signal fidelity,particularly by decreasing bandwidth. As will be appreciated by oneskilled in the art, the probe tip and probe body have a parasiticcapacitance and inductance (“parasitics”). The amount of conductivematerial in the signal path is directly proportional to the magnitude ofthe parasitic components. In the past, test probe parasitics have notbeen as significant a problem as they are today. The reason is that testprobe parasitics are generally not a significant problem at lowfrequencies. At the high frequencies (e.g., 6 GHz and higher) that arecommonplace in circuits today, even a small increase in parasiticcapacitance in the signal path will significantly increase the loadplaced on the circuit under test. In addition, at high frequencies, theeffects of test probe parasitics on signal fidelity significantlyincrease.

Test probes that have connectors that employ a threaded connectiongenerally have more metal than is used in pliant connectors, thus suchconnectors have relatively high parasitics. Test probes that haveconnectors that employ springs or elastomers to join mechanically theprobe body with the probe tip have lower (though still high) parasitics.However, the level of parasitics found in spring or elastomer connectorshave the additional problem of being variable. As the relative positionsand shape of the springs as well as the position of the probe tip changein response to forces encountered by the probe tip, the amount ofparasitics also varies. The surface area of the probe tip that is incontact with the socket can also change in response to these forces,changing the parasitics of the probe. It is all but impossible tooptimize a test probe design to compensate for variable parasitics.

Yet another general problem with the use of removable tips is theinsertion of an additional distance or electrical length that isrequired for the repeatably removable connector. To avoid distortion, itis especially important to minimize this distance when measuring highfrequency signals for which the corresponding wavelengths are not largecompared with the electrical length.

In differential test probes, there are two probe tips and two signalpaths each of which couples a separate signal to one of two inputs of adifferential amplifier. If the differential test probe has removableprobe tips that employ spring or elastomer connectors, the connector ineach tip adds parasitics that vary with pressure against the respectiveprobe tip. This causes signal fidelity errors that differ for each ofthe two signal paths. Therefore, there is a signal fidelity error in thedifferential signal that varies as a result of the respective pressuresapplied at each connector. As mentioned, it is all but impossible tooptimize a test probe design to compensate for variable parasitics.

Accordingly, there is a need for a modular active test probe andremovable tip module therefor that optimizes test probe performance.

BRIEF SUMMARY OF THE INVENTION

Disclosed is a modular active test probe and removable tip moduletherefor. Within the scope of the invention, there is a probe tip modulecomprising a first probe tip adapted for probing a circuit under test toreceive a signal therefrom. The probe tip module includes an amplifierhaving a first input solidly connected to the probe tip, an outputconnected to an output connector, and a housing for supporting the probetip, the amplifier, and the output connector. A probe body iscooperatively adapted with the housing for repeatably removablyreceiving at least the output connector.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a pictorial view of a typical prior art active test probe.

FIG. 2 is a partial sectional view of the prior art active test probeshown in FIG. 1.

FIG. 3 is a sectional view of a single tip embodiment of a tip modulefor a modular active test probe according to the present invention.

FIG. 4 is a sectional view of the tip module of FIG. 3 attached to amodular active test probe body according to the present invention.

FIG. 5 is a partial sectional view of a connector for the modular activetest probe body of FIG. 4.

FIG. 6 is a sectional view of a differential embodiment of a modularactive test probe and removable tip module therefor according to thepresent invention.

FIG. 7 is a block diagram showing three testing instruments and threedifferent plug and socket connector systems that mate with associatedcompensation boxes.

DETAILED DESCRIPTION OF THE INVENTION

As context for the present invention, a typical prior art active testprobe 20 is shown in FIGS. 1 and 2. The probe 20 is used, for example,to probe test pins on a circuit board or the leads of an integratedcircuit for a signal, and to transmit the signal to a signal measuringor display apparatus (“signal measuring apparatus”) such as anoscilloscope. The probe 20 has an elongate, flexible test probe cable24, typically at least 12″ long, to allow convenient access to remotecircuits under test. The cable 24 is adapted for repeatably removablemechanical and electrical connection to the signal measuring apparatusat one end, typically at a compensation box 22 that may includecompensating circuitry and a power supply and that is adapted to pluginto the measuring apparatus via a coax connector.

The other end of the cable 24 is mechanically and electrically connectedto a probe end 21, for probing the circuit under test by making intimatecontact with the test pins, leads, or other circuit structures. Anamplifier 23 for amplifying the signal received from the circuit undertest is typically provided in the probe end.

The probe end 21 includes a probe body 26, an end cap 28, and aconductive probe tip 30. The end cap 28 and the probe tip 30 are anintegral assembly (“tip assembly”). However, as a desirable feature ofsome prior art test probes, the tip assembly is adapted to be repeatedlyremoved from and attached to the probe body 26, meaning that the tipassembly can be removed from and attached to the probe body a largenumber of times without degrading the performance of the connection.

Referring in addition to FIG. 2, the probe body 26 of the prior artprobe 20 includes a compliant connector 36 for removably receiving theprobe tip 30. Compliance is provided by springs 38 and 40. The connector36 is electrically coupled to an electrical circuit 42 that includes theamplifier 23. The connector 36 and the springs 38 and 40 are alsotypically formed of metal that, as mentioned above, adds to theparasitics and electrical length of the test probe. The probe tip 30 isan elongated electrically conductive member, typically formed of metal.

In FIG. 2, the tip assembly is shown attached to the probe body 26. Thetip assembly is held in the attached position by the springs 38 and 40acting on the probe tip 30. The tip assembly can thereby be repeatedlyremoved and re-attached to the probe body 26. However, the springs 38and 40 do not provide a mechanically rigid connection. When the probetip 30 is pressed against a test point, it can move or wiggle (asindicated by arrows 60, 62) causing the parasitic inductance andcapacitance to change as the arrangement or shape of the springs 38 and40 and as the amount of surface area of the probe tip 30 in contact withthe springs 38 and 40 and the connector 36 changes.

The circuit 42 is adapted to compensate for the particular geometry ofthe probe tip 30. If the probe tip 30 is replaced with a probe tiphaving a different geometry, the circuit 42 will not optimallycompensate the replacement probe tip.

The probe 20 is typically sold as an integral unit with the compensationbox 22 at a first end of the cable 24 and the probe end 21 at a secondend of the cable 24. The compensation box 22 is generally specificallydesigned to mate with a particular model plug and socket connector of atesting instrument. Exemplary plug and socket connector systems include,for example, BNC, BMA, SMP, SMA, N-connector, and systems to bedeveloped in the future. The shapes and/or electronic characteristics ofthe various plug and socket connector systems vary considerably suchthat a compensation box 22 designed for a first plug and socketconnector system would not work with a compensation box 22 designed fora second plug and socket connector system. Some plug and socketconnector systems are industry standards and others are proprietary, butthey do evolve and change. Because the compensation box 22 is integralwith the probe 20, the entire probe, therefore, may only be used withtesting instruments that use the associated plug and connector system.

Further, the probe end 21 is generally specifically designed for aparticular purpose. For example, the probe end 21 may be a currentprobe, an active probe, a passive probe, an optic probe, wireless probe,or a type of probe to be developed in the future. (The probe ends may,of course, have various types of integral or replaceable probe tips 30.)Because the probe end 21 is integral with the probe 20, the entire probe(including the compensation box 22) must be changed to reflect theuser's intended purpose for the probe 20.

The significance of this is shown if a user has three testinginstruments a, b, and c each with a different plug and connector system.If the user desires to have a current probe, an active differentialprobe, and an optic probe that may be used with each of the testinginstruments, the user would be required to purchase nine (9) separateprobes 20. At prices ranging between $1,000 and $9,000, this can resultin a significant investment.

FIGS. 3–6 show detailed exemplary embodiments or features of the presentinvention and will be discussed below. The broad concept, however, willbe described below in connection with FIG. 7.

Turning now to FIGS. 3 and 4, a preferred single tip embodiment of amodular active test probe and removable tip module therefor according tothe present invention are shown. Particularly, FIG. 3 shows a removabletip module 128 according to the present invention and FIG. 4 shows amodular active test probe 100 having the tip module 128 attached to atest probe body 126.

The removable tip module 128 has a circuit 142 that is adapted tooptimize the performance of the test probe 100 for the tip module 128.Importantly, the circuit 142 is provided as part of the tip module 128so that it may be removably attached to the probe body 126 together withthe tip module 128. An outstanding feature of the present invention isthat the tip module 128 may be removed from the probe body 126 andreplaced with one or more an alternative tip modules, wherein eachalternative replacement tip module has unique requirements forcompensation as well as a unique circuit 142 adapted to optimize theperformance of the test probe for the alternative replacement tipmodule.

An output of the circuit 142 is provided at a tip module connector 155for repeatably removable connection of the tip module 128 to the probebody 126. In one preferred embodiment, the module connector 155 isrelatively low impedance point, e.g., 50 ohms. The tip module connector155 comprises an output connector 154 of the tip module 128 and a matinginput connector 164 in the probe body 126. This connection may be anytype of repeatably removable connection known in the art. In particular,this repeatedly removable connection may be made according to anystandard connectors known in the art, such as SSMP and MMCZ connectorsas well as connectors yet to be developed. An outstanding feature of theembodiment of the present invention in which the module connector 155 isrelatively low impedance point is a reduction in the effect of theparasitics resulting from the connection between the output connector ofthe tip module and the input connector of the probe body.

In contrast to the connection between the probe body 126 and the tipmodule 128, the probe tip 162 is not adapted for repeatably removableattachment. In fact, the probe tip 162 cannot be decoupled from thecircuit 142 without breaching the connection, such as by cutting orbreaking the connection. Such a connection is referred to herein as a“solid” connection. A solid connection between disparate parts may beachieved, e.g., by soldering, welding, joining with an electricallyconductive epoxy, or any other method known in the art for forming asolid connection. The solid connection is yet another outstandingfeature of the present invention in that, at the input 159, the variableparasitics are eliminated by eliminating the pliancy found in spring andelastomer sockets and the total parasitics are minimized because lessconductive material is used than is generally used with connectors. In apreferred embodiment, the circuit 142 includes one or more amplifiers111 to provide a high impedance input 159. The relatively high impedanceof the input provides the advantage of minimally loading the circuit. Inthis embodiment, it is especially important to minimize parasiticelements and, therefore, the solid connection of the present inventionis particularly advantageous.

Preferably, the probe tip 162 is soldered to a circuit board 158 towhich the circuit 142 is also solder connected. A signal conductor 160between the probe tip and the circuit 142 is provided as a trace on thecircuit board 158. The circuit board 158 may be formed as isconventional in the art, e.g., of FR4 or polyimide.

The circuit 142 also preferably includes a compensating circuit portion(not shown) to compensate for the parasitics of the tip module. Suchcircuits are well known in the art; however, they have not heretoforebeen provided in a tip module adapted to be repeatedly removed from andattached to a probe body. The provision of compensation for the tipmodule in the tip module ensures that optimum signal fidelity may beachieved for any tip module 128 used with the probe body 126.

Preferably, the tip module connector 155 provides high frequency,transmission line characteristics for the output of the circuit 142. Inthe embodiment of the invention shown, this is accomplished by providingthe output connector 154 of the tip module with an elongate metal pin,and the input connector 164 for receiving the output connector 154 withan appropriately terminated coaxial cable as shown in FIG. 5. In thatcase, the input connector 164 includes an inner conductor 150 for makingintimate contact with the connector 154, an outer conductor 148 employedfor shielding, and an insulator 152 disposed therebetween. However, itis an outstanding feature of the invention that any other connectorconfiguration may be employed for the tip module connector 155, such asSSMP, BMA, SMB, MMCX, and SSMB and the effect of connection parasiticswill be reduced due to the unique features of the tip module.

The tip module 128 includes a housing 129 adapted to hold and supportthe probe tip 162 and to support or contain the circuit 142, the outputconnector 154, the circuit board 158, and other desired test modulecomponents such as a memory (similar to memory 270 in FIG. 6) forstoring, e.g., identifying or parametric information, and calibrationcircuitry. Preferably, the housing 129 holds the probe tip 130 and thecircuit 142 in fixed dispositions relative to the output connector 154.This arrangement advantageously eliminates variable parasitics thatwould arise if the relative motion between these components werepermitted.

In addition, the tip module includes a mechanical connector 169 formechanically attaching the tip module to the probe body 126. In theexample shown, the mechanical connector 169 includes a screw thread 166for mating with a complementary screw thread 166 on the probe body;however, a snap fitting or any other means for repeatably removablyattaching the tip module 128 to the probe body 126 may be employed.

Turning to FIG. 6, a removable differential tip module 228 according tothe present invention is shown attached to a test probe body 226. Thetest probe body 226 may be identical to the probe body 126 describedabove. The tip module 228 includes two electrically conductive probetips 262 coupled to a circuit 242 through respective signal conductors260 and 261. The circuit 242 includes a differential amplifier foramplifying the signals received via the signal conductors. The circuit242 transmits a differential signal to a tip module connector 255 thatmay be constructed identically to the tip module connector 155 describedabove (e.g. including an output connector 154 that mates with a matinginput connector 164 that includes an inner conductor 150, an outerconductor 148, and an insulator 152). The circuit 242 is preferablysoldered to a circuit board 258 having traces functioning as the signalconductors 260 and 261. A mechanical connector 269 (e.g. screw threads266) may also be used for mechanically attaching the tip module 228 tothe probe body 226.

The circuit board 258 preferably includes a semi-flexible or bendableportion 230 which may be formed integrally by decreasing the width (inthe plane of FIG. 5), or the thickness of the board. The probe tips 262are soldered to the portion 230. The portion 230 may flex or bend alimited amount with respect to the tips 262 and at the dashed line 272while minimizing parasitics.

Like the tip module 128 described above, the tip module 228 may includea memory 270 and a communications bus 274 for communicating with theprobe body 226. The memory may include information identifying the tipmodule, or parametric data defining the electrical characteristics ofthe tip module. Such information may be used by additional circuitry inthe probe body, or by the measuring apparatus to which the probe isconnected.

The probe tips 262 need not be identical, and the tips 162 and 262 mayhave any desired shape. Where it is desired to replace a broken ordamaged tip, it is an outstanding feature of the invention that the tipmodule can be replaced without necessitating replacement of the entireprobe 200, as is required for active or passive probes employingnon-replaceable tips, and without losing the matching provided betweenthe amplifier and the probe tip as in prior art active probes employingreplaceable tips.

It may now be appreciated that the present invention provides for anumber of advantages, which may be enjoyed separately or in combination.For example, the amount of conductive material is minimized in thecritical signal path between the test point and the amplifier input. Asmentioned, this is particularly advantageous when measuring highfrequency signals. Further, the solid connections in this criticalsignal path also minimize variation in parasitics as a result of theforces encountered by the probe tip during probing of the circuit.Further, the use of solid connections in this critical signal pathensures that test probe parasitics do not vary as a result of varyingthe force applied to the probe tip. Still further, circuitry within thetip module is optimized to compensate for the unique parasitics of thatspecific tip module. Replacing the tip module also replaces thecompensation so that optimum signal fidelity is maintained. Anadditional advantage of the differential embodiment of the invention isthat the parasitic inductance and capacitance of each probe tip ismatched so that differential signal error is also minimized.

While the removable tip module of the present invention has beendescribed in only terms of a single-ended and differential voltage probetip module, it should be understood that other embodiments in which theprobe tip module may comprise any type of probe tip known in the art arecontemplated. For example, it is specifically contemplated that the tipmodule may be a current probe, an optical probe, or any other type oftransducer known in the art. In addition, it is contemplated that thetip module be a standard connector adapted to couple with anotherstandard connector. Further, while the circuit 142, 242 has beendescribed in terms of having compensating circuitry, it will beappreciated that this circuitry is optional. It is contemplated that theamplifier may be designed so that compensation circuitry is unnecessary.Further, it is contemplated that the input to the amplifier may be atransmission line structure as described in U.S. patent application Ser.No. 10/261,829 (entitled Transmission Structure for Electrical TestProbe here), said reference is hereby incorporated by reference in itsentirety.

The embodiments discussed above are meant to be exemplary and, althoughcertain features are unique in and of themselves, the inventors of thepresent invention assert that the broad concept shown in FIG. 7 is alsounique.

FIG. 7 shows three testing instruments 320 a, 320 b, and 320 c, which,for purposes of this disclosure, are assumed to have three differentplug and socket connector systems that mate with the associatedcompensation box 322 a, 322 b, and 322 c. Each compensation box 322 a,322 b, and 322 c is attached via a cable or other connection means to atest probe body 326 having a controller 327 therein. It should be notedthat although shown as a single embodiment of a test probe body 326, itis possible that there are alternative or multiple types of test probebodies. Similarly, it should be noted that although shown as a singleembodiment of a controller 327, it is possible that there arealternative or multiple types of controllers. The controller 327 may beindividually programmed to provide information about the compensationbox 322 a, 322 b, and 322 c, cable, and/or test probe body 326. Thecontroller 327, however, is designed to communicate with and obtaininformation from the circuit 342 a, 342 b, or 342 c of the respectivetip modules 328 a, 328 b, and 328 c. It should be noted that althoughshown as three separate circuits 342 a, 342 b, 342 c, it is possiblethat the circuits 342 a, 342 b, 342 c are identical, but programmeddifferently to reflect the specific characteristics of the respectivetip modules 328 a, 328 b, and 328 c. As shown by the lead lines, any ofthe tip modules 328 a, 328 b, 328 c may be connected to any of thecompensation box/test probe body combinations (or platforms) 322 a/326,322 b/326, and 322 c/326.

The significance of this is shown if a user has three testinginstruments 320 a, 320 b, and 320 c and the user desires to have acurrent probe tip module 328 a, an active differential probe tip module328 b, and an optic probe tip module 328 c that may be used with each ofthe testing instruments. In this case, instead of being required topurchase nine (9) separate probes 20, the user could produce exactlywhat he needs: three compensation box/test probe body platforms 322a/326, 322 b/326, 322 c/326, a current probe tip module 328 a, an activedifferential probe tip module 328 b, and an optic probe tip module 328c. Further, if the user purchases a fourth testing instrument, he wouldonly need to purchase an associated compensation box/test probe bodyplatform and he could still use the current probe tip module 328 a,active differential probe tip module 328 b, and optic probe tip module328 c. Similarly, a new tip module could be used with any of thecompensation box/test probe body platforms 322 a/326, 322 b/326, 322c/326.

In one preferred embodiment, the compensation box/test probe bodycombinations (or platforms) have the ability to enhance or add featuresto the testing instrument and/or the tip modules. For example, oldergeneration testing instruments would not be able to turn off a tipmodule that was overheating. However, the platform can be implemented toinclude this feature. Using the platforms the tip modules can be updatedto include new features.

The features discussed in connection with FIG. 7 are also shown anddescribed in connection with FIGS. 3–6. For example, as discussed above,“an outstanding feature of the present invention is that the tip module128 may be removed from the probe body 126 and replaced with one or morean alternative tip modules, wherein each alternative replacement tipmodule has unique requirements for compensation as well as a uniquecircuit 142 adapted to optimize the performance of the test probe forthe alternative replacement tip module.”

Based on the information present in this specification, it can be seenthat one advantage of the present invention is the forward and backwardcompatibility without having to purchase all new equipment. Further, bychanging tip modules 328 a, 328 b, and 328 c, any type of signal may bemeasured with any testing instrument 320 a, 320 b, 320 c. Still further,because of the modular configuration, the controller 327 and/or circuit342 a, 342 b, 342 c may be implemented as firmware that may be easilyupdated (perhaps even as a software upgrade). The present invention alsooffers better signal characteristics, a smaller product, and otheradvantages discussed throughout this disclosure.

The terms and expressions that have been employed in the foregoingspecification are used as terms of description and not of limitation,and are not intended to exclude equivalents of the features shown anddescribed or portions of them. The scope of the invention is defined andlimited only by the claims that follow.

1. A modular active test probe for probing a circuit and transmitting atleast one signal therefrom to a signal measuring apparatus, comprising:(a) a probe tip module comprising a first probe tip adapted for probingthe circuit to receive a first signal, an amplifier having an inputhaving a first impedance solidly connected to said probe tip, an outputhaving a second impedance connected to an output connector, and ahousing for supporting said probe tip, said amplifier, and said outputconnector; and (b) a probe body cooperatively adapted with said housingfor repeatably removably receiving said output connector.
 2. The testprobe of claim 1, wherein said first impedance is a high impedance incomparison with the output impedance of a test point in the circuitwhere said first signal is sampled.
 3. The test probe of claim 1,further comprising an elongate, flexible test probe cable adapted formechanical connection to said probe body, repeatably removablemechanical and electrical connection to the signal measuring apparatus,and electrical connection between said output connector and the signalmeasuring apparatus.
 4. The test probe of claim 3, wherein said secondimpedance is a relatively low impedance and is matched with theimpedance of said test probe cable.
 5. The test probe of claim 1,wherein said probe body is cooperatively adapted with said housing formechanically repeatably removably receiving said housing.
 6. The testprobe of claim 5, wherein said housing includes screw threads formechanically repeatably removably receiving said housing.
 7. The testprobe of claim 1, further comprising a circuit board to which saidamplifier is solder connected.
 8. The test probe of claim 7, whereinsaid probe tip is solder connected to said circuit board.
 9. The testprobe of claim 8, wherein said circuit board includes a trace forconducting the signal from said probe tip to said amplifier.
 10. Thetest probe of claim 1, further comprising a compensating circuit adaptedto compensate for selected electrical characteristics of said tipmodule.
 11. The test probe of claim 1, further comprising a compensatingcircuit adapted to compensate for selected electrical characteristics ofsaid tip module.
 12. The test probe of claim 1, comprising a secondprobe tip mechanically adapted for probing the circuit to receive asecond signal, wherein said amplifier includes a second input solidlyconnected to said second probe tip, said second input having a thirdimpedance, and wherein said amplifier is adapted to provide adifferential signal derived from said first and second inputs on saidoutput.
 13. The test probe of claim 12, further comprising acompensating circuit adapted to compensate for selected electricalcharacteristics of said tip module.
 14. The test probe of claim 12,wherein said compensating circuit is adapted to compensate for selectedelectrical characteristics of each said first and second probe tips. 15.The test probe of claim 12, further comprising a circuit board having abendable portion, wherein said amplifier is solder connected to saidcircuit board and said first and second probe tips are solder connectedsaid bendable portion of said circuit board.
 16. The test probe of claim15, wherein said circuit board includes a first trace for conductingsaid first signal from said first probe tip to said amplifier and asecond trace for conducting said second signal from said second probetip to said amplifier.
 17. The test probe of claim 16, wherein saidfirst trace comprises a first transmission line and said second tracecomprises a second transmission line.
 18. The test probe of claim 1,wherein said first probe tip is adapted to measure a current signal. 19.The test probe of claim 1, wherein said first probe tip is adapted tomeasure an optical signal.
 20. The test probe of claim 1, wherein saidfirst probe tip is adapted to couple with a connector.
 21. The testprobe of claim 1, wherein said probe tip module includes a memory. 22.The test probe of claim 1, wherein said test probe is used for providinga functional connection between said signal measuring apparatus and saidcircuit and transmitting at least one signal therebetween, each signalmeasuring apparatus having a specific signal measuring apparatusconnection scheme, said test probe further comprising: (a) acompensation box functionally interconnected to said probe body; (b)said compensation box having a compensation box connection schemeadapted to mate with an associated signal measuring apparatus connectionscheme such that said compensation box is configured to mate with anassociated signal measuring apparatus; (c) said probe tip module havingan identification circuit suitable for providing identification datasignals regarding the probe tip module in which identification circuitis positioned; and (d) said probe body having a controller suitable forcommunicating with said identification circuit and said signal measuringapparatus; (e) wherein said signal measuring apparatus may be connectedto an associated probe body which may be connected to any said at leastone probe tip module.
 23. The test probe of claim 22 further comprising:(a) a plurality of signal measuring apparatus; (b) a plurality of probebodies, each probe body associated with a respective one of saidplurality of signal measuring apparatus; and (c) a probe tip module,said probe tip module interconnectable with any of said plurality ofprobe bodies.
 24. The test probe of claim 22 further comprising: (a) asingle signal measuring apparatus; (b) a probe body associated with saidsingle signal measuring apparatus; and (c) a plurality of probe tipmodules, each of said plurality of probe tip modules interconnectablewith said probe body.
 25. The test probe of claim 1, wherein signalmeasuring apparatus is a testing instrument.
 26. A modular active testprobe for probing a circuit and transmitting at least one signaltherefrom to a signal measuring apparatus, said test probe comprising:(a) a probe tip module comprising (i) a first probe tip adapted forprobing the circuit to receive a first signal; (ii) an amplifier havingan input having a first impedance and an output having a secondimpedance; (iii) said amplifier input solidly connected to said probetip to form a solid connection therebetween; (iv) said amplifier outputconnected to an output connector; and (v) a housing for supporting saidprobe tip, said amplifier, and said output connector; and (b) a probebody cooperatively having an input connector for repeatably removablyreceiving said output connector to form a repeatably removableconnection therebetween.